Thread cutters for sewing machines



Feb. 14, 1967 A. P. STEINER 3,33,@5

THREAD CUTTERS FOR SEWING MACHINES Filed Dec. 7, 1964 INVENTOR. Adam P. Sieiner ATTORNEY United States Tatent O 3 303,805 THREAD CUTTER TOR SEWZNG MACHINES Adam P. Steiner, Union, NJ, assignor to The Singer Company, New York, N.Y., a corporation of New Jersey Filed 33cc. 7, 1964, Ser. No. 416,260 4 filaims. (Cl. 112-252) This invention relates to thread cutters for sewing machines and more particularly to a thread cutter for automatically severing concatenated threads form-ed between successively stitched articles of work material.

A United States patent of Enos, No. 2,747,533, granted May 29, 1956, discloses a thread cutter having a first cutting edge formed on the leading edge of the feed dog. The leading edge of the feed dog, and hence the cutting edge, lies in a plane defined by the tops of the feed teeth of the feed dog. A second cutting edge is formed on a ledger blade mounted on the presser foot. The thread cutter of Enos works well on lockstitch machines. However, on chain stitch machines, the action of the thread cutter has been somewhat less than desirable. The foregoing phenomenon results from the fact that in chain stitch sewing the looper thread cannot be pulled up into the work material as in lockstitch sewing because of the inherent feature of chain stitch sewing in which enchained loops of thread are formed on the underside of the work material. As the feed dog tilts upwardly in its elliptical path to begin each work feeding stroke, the cutting edge on the feed dog tends to lacerate the thread chain formed on the bottom surface of the work material because the cutting edge is the first part of the feed dog to contact the work material.

It is, therefore, a primary object of this invention to provide a thread cutter for automatically severing concatenated threads formed between successively stitched articles of work material which will function well on chain stitch machines, as well as on lockstitch machines, without damaging either the work material or stitches formed in the work material.

Another object of the invention is to provide an improved means for adjusting the alignment of the cutting edges of the thread cutter.

Briefly, the objects of the invention are accomplished by forming a bevel on the leading portion of the feed dog in advance of the feed teeth. The bevel positions the leading edge of the feed dog and hence the cutting edge on the leading edge far enough below the plane defined by the tops of the feed teeth so that the cutting edge can never be the highest portion of the feed dog during the time when any portion of the feed dog is above the top surface of the work-supporting bed as the feed dog orbits in its elliptical path. Therefore, the cutting edge cannot lacerate thread chains formed on the bottom surface of work material. In addition, the ledger blade on the presser foot is pivoted downwardly at a greater angle than that disclosed in the patent of Enos so that only the leading edge portion of the feed dog can contact the fiatbottomed bearing surface extending forwardly from the cutting edge on the ledger blade. In other words, the fiat-bottomed bearing surface is positioned at an acute angle with respect to a horizontal plane which is never less than the maximum acute angle formed by the bevel with the horizontal plane during the time when any portion of the feed dog is above the top surface of the worksupporting bed.

Other objects and a fuller understanding of the invention may be had by referring to the following descri tion and claims, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a head-end elevational view of a sewing machine having a feed dog and a presser foot incorporating a thread cutter of the invention;

FIG. 2 is an enlarged longitudinal cross-sectional view of the presser foot and feed dog of FIG. I with the thread cutter in cutting position;

FIG. 3 is a bottom plane view of the presser foot of FIG. 2;

FIG. 4 is a rear elevational view of the presser foot of FIG. 2;

FIG. 5 is a further enlarged detail view of the feed dog and presser foot of FIG. 2 with work material interposed between the feed dog and the presser foot; and

FIG. 6 is a schematic view of the angular relationships between the critical surfaces of the thread cutter with the angles somewhat exaggerated for clarity.

With reference to the drawings, the invention is illustrated as incorporated in a two-thread chain stitch machine. The invention may be embodied in many different types of chain stitch machines or, indeed, in a lockstitch machine, and the two-thread chain stitch machine is employed merely by way of example.

The two-thread chain stitch machine has a work-supporting bed It) and a sewing head 11 rising from one end of the work-supporting bed. Although only partially shown, the sewing head 11 is conventional and includes a hollow standard rising from one end of the work-supporting bed and a hollow bracket arm connected to the top of the standard and extending transversely over the worksupporting bed.

Mounted in the work-supporting bed 10 and the sewing head 11 are stitch-forming mechanisms. The upper stitch-forming mechanism includes a thread-carrying needle 12 which is secured to an endwise reciprocating needle bar 13. The needle bar is mounted in the sewing head for reciprocation by conventional mechanisms (not shown). The lower stitch-forming mechanism includes a thread-carrying looper 14 which is secured to a looper bar 15. Through the use of conventional mechanisms the looper has imparted to it endwise loop-seizing and loop-shedding movements and lateral needle-avoid motions.

Removably secured to a presser bar 17 by means of a clamping screw 18 is a presser foot, indicated generally at 19. The presser bar 17 is mounted in the sewing head 11 in a manner well known.

The presser foot 19 includes a shank 2t? and a sole plate 21. Connected to the rear of the shank of the presser foot by means of a screw 22 and a pivot pin 23, respectively, are a spring retainer bracket 24 and a spring abutment bracket 25. The spring retainer bracket 24 is formed with a bore 26 to house a body portion 27 of a shouldered pin 28 and the spring abutment bracket 25 has a spring-receiving socket 29. A coiled compression spring 30 is mounted on a pilot portion 31 of the shouldered pin 28 and extends between a shoulder 32 of the pin 28 and a face 33 of the spring-receiving socket 29 in the spring abutment bracket 25. The downward bias or force applied to the spring abutment bracket 25 by the coiled compression spring 3% is regulated by sliding the pin 28 lengthwise of the bore 26 and then securing the pin by means of a setscrew 34 in a threaded bore 35 transversely communicating with the bore 26 in the spring retainer bracket 24. A fiat 36 is formed in the circumference of the body portion 27 of the shouldered pin 28 against which the setscrew 34 seats. The position of the shouldered pin in the spring retainer bracket 24 determines the amount of downward force applied to the spring abutment bracket 25. A tongue 37 formed on the rear of the sole plate of the presser foot constitutes a stop means to limit the downward movement of the spring abutment bracket 25.

Held on the spring abutment bracket 25 is a member which serves as a ledger bar 38. The ledger bar has a hole 39 which embraces a portion 40 of the spring abutment bracket having a circular cross section. A transverse threaded bore 41 in the ledger bar communicates with the hole 39 which embraces the spring abutment bracket, and a setscrew 42 in the threaded bore 41 provides a means for atfixing the ledger bar 38 to the spring abutment bracket 25 and for adjusting the angular orientation of the ledger bar around the portion 40 of the spring abutment bracket.

Connected to the bottom of the ledger bar 38 is a U-shaped ledger blade 43 having a sharpened cutting edge 44 formed in the throat of the U. The ledger blade 43 may be composed of a metallic carbide such as is used in metal-cutting tools and may be connected to the ledger bar 38 preferably by brazing or by silver solder.

Mounted in the work-supporting bed is a fourmotion feed dog 45. The feed dog is secured to a feed bar 46 by means of a screw 47. Feed-advance motion is imparted to the feed dog through a feed-advance rock shaft 48 and mechanisms well known while feed-lift motion is imparted to the feed dog through a feed-lift rock shaft 49. To receive motion from the feed-lift rock shaft, the feed-bar is forked as at 50 and embraces a roller 51 which is connected to a rock arm 52. The rock arm is in turn connected to the feed-lift rock shaft 49.

Two rows of feed teeth 53 and 54 are formed in the top of the feed dog 45. The feed dog is positioned in the work-supporting bed 10 so that the rows of feed teeth are in line with corresponding slots 55, of which only one is shown, formed in a throat plate 56 when the throat plate is secured to the work-supporting bed in a manner well known.

Carried on the leading portion of the feed dog 45 is a cutter blade 57 having a sharpened cutting edge 58 formed along a leading edge. The cutter blade 57 may be composed of the same material as the ledger blade 43 or it may be composed of a cobalt material, such as is used in metal-cutting tools. The use of a cobalt material affords numerous advantages over the use of a metallic carbide in that a cobalt cutter blade is selfsharpening when used in opposition to a carbide ledger blade and a cobalt cutter blade can be connected to the feed dog by a soft solder instead of requiring brazing with a hard solder.

In order to prevent the cutting edge on the feed dog 45 from lacerating the bottom surface of work material 59 interposed between the presser foot 19 and the feed dog, or lacerating a thread chain 60 formed on the bottom surface of the work material, the cutter blade 57 has a bevel 61. The bevel positions the leading edge of the feed dog and hence the cutting edge 58 formed on the leading edge far enough below a plane AA defined by the tops of the feed teeth 53 and 54 so that the cutting edge 58 can never be the highest portion of the feed dog during the time when any portion of the feed dog is above the top surface of the work-supporting bed 10 as the feed dog orbits in its elliptical four-motion path. In other words, as shown in FIG. 6, the angle B of the bevel is never less than the maximum angle C that the plane AA can make with the plane DD of the top surface of the work-supporting bed. In practice, the angle B is from 3 to 10 degrees in a run of less than one-eighth of an inch. It is within the scope of the invention to position the cutting edge 58 of the feed dog below the plane AA of the tops of the feed teeth by other means than by the bevel 61 on the cutter blade 57. For example, the cutter blade 57 could have a concave curved surface in lieu of the bevel 61 or could he stepped so that the cutting edge 58 lies below the plane AA.

In operation, when the work material 59 is interposed between the presser foot 19 and the feed dog 45,

the thread cutter is rendered inoperative. The U-shaped ledger blade 43 merely rides on the top surface of the work material 59 without damaging the work material. The cutting edge 44 formed in the throat of the U never contacts the work material because the ledger blade 43 is held at an angle with respect to the top surface of the work material 59 by the spring abutment bracket 25. The downward force exerted by the coiled compression spring 30 on the spring abutment bracket 25, and hence the pressure of the ledger blade 43 on the work material can be regulated by the setscrew 34. Because of the bevel 61 on the cutter blade 57, the cutting edge 58 thereof is far enough below the plane AA of the tops of the feed teeth 53 and 54 so that the cutting edge 58 cannot lacerate the bottom surface of the work material 59, or stitches formed in the work material, even at the position of maximum tilt of the feed dog as the feed dog tilts upwardly in its elliptical four-motion path to begin a feed stroke. The top portion of the bevel 61 merely brushes by the bottom surface of the work material 59 until the feed teeth 53 and 54 grip the work material to begin the feed stroke.

However, after the work material 59 has passed beyond the ledger blade 43, the ledger blade can drop down under the impetus of the coiled compression spring 30 to cooperate with the cutter blade 57 on the feed dog automatically to sever the thread chain formed from the concatenation of looper thread 62 between successive articles of work material 59. The spring abutment bracket 25 is pivoted on the shank 20 of the presser foot 19 so as to extend downwardly at a greater angle than in the previously mentioned patent of Enos, No. 2,747,- 533, so that the cutting edge 44 on the ledger blade 43 can coact properly with the relocated cutting edge 58 on the feed dog. As previously described, the tongue 37 formed on the sole plate of the presser foot limits the downward movement of the spring abutment bracket 25 by blocking the ledger bar 38.

The leading edge of the feed dog on which the cutting edge 58 is formed is wider than the throat of the U- shaped ledger blade 43, and a fiatbottomed bearing surface represented by limb portions 63 and 64 (FIG. 3) of the ledger blade 43 extends forwardly from the cutting edge 44 of the ledger blade. In a thread cutting stroke, the cutting edge 58 on the feed dog first contacts the limb portions 63 and 64 of the ledger blade and entraps the concatenated threads 60 in the throat of the U. The cutting edge 58 on the feed dog then walks the ramp of the inclined limb portions 63 and 64 of the ledger blade 43 until it reaches the cutting edge 44 formed in the throat of the U-shaped ledger blade. When the cutting edge 58 on the feed dog reaches the cutting edge 44 in the throat of the U, a shearing action occurs and the concatenated threads 60 are cut. The angle E that the plane F-F of the bottoms of the limb portions 63 and 64 of the ledger blade makes with a plane GG parallel to the plane DD of the top surface of the work-supporting bed 10 is never less than the maximum angle H that the plane II of the bevel 61 makes with the plane GG during the time when any portion of the feed dog is above the top surface of the Work-supporting bed. Therefore, the leading edge of the feed dog with the cuting edge 58 is the only portion of the feed dog that can contact the limb portions 63 and 64 of the ledger blade 58. It is understood that contact may occur when the feed dog is tilted upwardly, when the feed dog is horizontal, or when the feed dog is tilted downwardly. The foregoing arrangement makes it possible to use looser manufacturing tolerances with consequential reduction in manufacturing costs. To compensate for manufacturing tolerances and subsequent wear of the cutting edges 44 and 58, the ledger bar is mounted on the circular cross-sectional portion 40 of the spring abutment bracket 25 so that the cutting edge 44 on the ledger blade 43 can be aligned with the cutting edge 58 on the feed dogi Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention.

Having thus set forth the nature of the invention, what is claimed herein is:

1 An automatic thread cutter in combination with a sewing machine having a work-supporting bed with at least one slot therein, a sewing head rising from the worksupporting bed, stitch forming means adapted to concatenate threads into stitches, a feed dog having at least one row of feed teeth and mounted in the work-supporting bed with the row of feed teeth in line with the slot in the work-supporting bed, said feed dog adapted to trace a cyclical path with the tops of the feed teeth above the top surface of the work-supporting bed during the upper work feeding portion of each cycle, and a presser foot mounted on the sewing head in opposition to the teeth of the feed dog, said automatic thread cutter comprising a leading edge formed on the feed dog in advance of the row of feed teeth and far enough below the plane defined by the tops of the feed teeth so that said leading edge can never be the highest portion of the feed dog during the time when any portion of the feed dog is above the top surface of the work-supporting bed, a first cutting edge formed on said leading edge, a ledger blade mounted on the presser foot, said ledger blade having a second cutting edge facing said first cutting edge and a bottom bearing surface extending forwardly from the second cutting edge, and means for moving the ledger blade downwardly to position said bottom bearing surface at such an angle that when any portion of the feed dog contacts said bottom bearing surface the leading edge of the feed dog must contact the bottom bearing surface.

2. An automatic thread cutter in combination with a sewing machine having a work-supporting bed with at least one slot therein, a sewing head rising from the worksupporting bed, stitch forming means adapted to concatenate threads into stitches, a feed dog having at least one row of feed teeth and mounted in the work-supporting bed with the row of feed teeth in line with the slot in the work-supporting bed, said feed dog adapted to trace a cyclical path with the tops of the feed teeth above the top surface of the work-supporting bed during the upper portion of each cycle, and a presser foot mounted on the sewing head in opposition to the teeth of the feed dog, said automatic thread cutter comprising a bevel formed on the leading portion of the feed dog in advance of the row of feed teeth at such an angle that the leading edge of the bevel is far enough below the plane defined by the tops of the feed teeth so that said leading edge can never be the highest portion of the feed dog during the time when any portion of the feed dog is above the top surface of the work-supporting bed, a first cutting edge formed on said leading edge, a ledger blade mounted on the presser foot, said ledger blade having a second cutting edge facing said first cutting edge and a flat-bottomed bearing surface extending forwardly from the second cutting edge, and means for biasing the ledger blade downwardly to position said flat-bottomed bearing surface at an acute angle with respect to a plane above and parallel to the top surface of the work-supporting bed which is never less than the acute angle formed by the bevel with said plane during the time when any portion of the feed dog is above the top surface of the work-supporting bed.

3. An automatic thread cutter in combination with a sewing machine having a work-supporting bed with at least one slot therein, a sewing head rising from the worksupporting bed, stitch forming means adapted to concatenate threads into stitches, a feed dog having at least one row of feed teeth and mounted in the work-supporting bed with the row of feed teeth in line with the slot in the work-supporting bed, said feed dog adapted to trace a cyclical path with the tops of the feed teeth above the top surface of the work-supporting bed during the upper portion of each cycle, and a pressure foot mounted on the sewing head in opposition to the teeth of the feed dog, said automatic thread cutter comprising a bevel formed on the leading portion of the feed dog in advance of the row of feed teeth forming an angle of from 3 to 10 degrees with the plane defined by the tops of the feed teeth in a run of less than one-eighth of an inch, said bevel having a leading edge, a first cutting edge formed on said leading edge, a ledger blade mounted on the presser foot, said ledger blade having a second cutting edge facing said first cutting edge and a flat-bottomed bearing surface extending forwardly from the second cutting edge, and means for biasing the ledger blade downwardly to position said flat-bottomed bearing surface at an acute angle with respect to a plane above and parallel to the top surface of the work-supporting bed which is never less than the acute angle formed by the bevel with said plane during the time when any portion of the feed dog is above the top surface of the work-supporting bed.

4. An automatic thread cutter in combination with a sewing machine having a work-supporting bed with at least one slot therein, a sewing head rising from the worksupporting bed, a stitch-forming means adapted to concatenate threads into stitches, a feed dog having at least one row of feed teeth and mounted in the work-supporting bed with the row of feed teeth in line with the slot in the work-supporting bed, said feed dog adapted to trace a cyclical path with the tops of the feed teeth above the top surface of the work-supporting bed during the upper portion of each cycle, and a pressure foot mounted on the sewing head in opposition to the teeth of the feed dog, said automatic thread cutter comprising a leading edge formed on the feed dog in advance of the row of feed teeth and far enough below the plane defined by the tops of the feed teeth so that said leading edge can never be the highest portion of the feed dog during the time when any portion of the feed dog is above the top surface of the worksupporting bed, a first cutting edge formed on said leading edge, a bracket having a portion with a circular cross-section pivot-ally mounted on the presser foot, a ledger blade member having a hole embracing the circular cross-sectional portion of the bracket and a threaded bore transversely communicating with said hole, said ledger blade member having a second cutting edge facing said first cutting edge and a bottom bearing surface extending forwardly from the second cutting edge, a setscrew threaded into the threaded bore in the ledger blade member for affixing the ledger blade member to the circular cross-sectional portion of the bracket and for adjusting the alignment of said first and second cutting edges, and means for biasing the bracket with the ledger blade member downwardly to position said bottom bearing surface at such an angle that when any portion of the feed dog contacts said bottom bearing surface the leading edge of the feed dog must contact the bottom bearing surface.

References Cited by the Examiner UNITED STATES PATENTS 2,293,236 8/1942 Anderson l12252 2,747,533 5/1956 Enos 1l2252 3,215,106 11/1965 Bono 112252 JORDAN FRANKLIN, Primary Examiner.

J. R. BOLER, Assistant Examiner. 

1. AN AUTOMATIC THREAD CUTTER IN COMBINATION WITH A SEWING MACHINE HAVING A WORK-SUPPORTING BED WITH AT LEAST ONE SLOT THEREIN, A SEWING HEAD RISING FROM THE WORKSUPPORTING BED, STITCH FORMING MEANS ADAPTED TO CONCATENATE THREADS INTO STITCHES, A FEED DOG HAVING AT LEAST ONE ROW OF FEED TEETH AND MOUNTED IN THE WORK-SUPPORTING BED WITH THE ROW OF FEED TEETH IN LINE WITH THE SLOT IN THE WORK-SUPPORTING BED, SAID FEED DOG ADAPTED TO TRACE A CYCLICAL PATH WITH THE TOPS OF THE FEED TEETH ABOVE THE TOP SURFACE OF WORK-SUPPORTING BED DURING THE UPPER WORK FEEDING PORTION OF EACH CYCLE, AND A PRESSER FOOT MOUNTED ON THE SEWING HEAD IN OPPOSITION TO THE TEETH OF THE FEED DOG, SAID AUTOMATIC THREAD CUTTER COMPRISING A LEADING EDGE FORMED ON THE FEED DOG IN ADVANCE OF THE ROW OF FEED TEETH AND FAR ENOUGH BELOW THE PLANE DEFINED BY THE TOPS OF THE FEED TEETH SO THAT SAID LEADING EDGE CAN NEVER BE THE HIGHEST PORTION OF THE FEED DOG DURING THE TIME WHEN ANY PORTION OF THE FEED DOG IS ABOVE THE TOP SURFACE OF THE WORK-SUPPORTING BED, A FIRST CUTTING EDGE FORMED ON SAID LEADING EDGE, A LEDGER BLADE MOUNTED ON THE PRESSER FOOT, SAID LEDGER BLADE HAVING A SECOND CUTTING EDGE FACING SAID FIRST CUTTING EDGE AND A BOTTOM BEARING SURFACE EXTENDING FORWARDLY FROM THE SECOND CUTTING EDGE, AND MEANS FOR MOVING THE LEDGER BLADE DOWNWARDLY TO POSITION SAID BOTTOM BEARING SURFACE AT SUCH AN ANGLE THAT WHEN ANY PORTION OF THE FEED DOG CONTACTS SAID BOTTOM BEARING SURFACE THE LEADING EDGE OF THE FEED DOG MUST CONTACT THE BOTTOM BEARING SURFACE. 